LTE is a mainstream technology developed from 3th Generation (3G) mobile communication technology to 4th (4G) mobile communication technology, which adopts Orthogonal Frequency Division Multiplexing (OFDM) and Multiple-Input Multiple-Output (MIMO) as its sole standard for wireless network evolution, and improves and enhances air access of 3G communication technology. LTE technology may provide peak rates of 100 Mbit/s downlink and 50 Mbit/s uplink in the bandwidths of 20 MHz, which may improve performance of cell-edge users, increase cell capacity and reduce system delay.
LTE network is a packet-switched network. Subject to performances of LTE-compatible mobile terminals and initial network configuration, if an LTE-compatible mobile terminal attempts to make a voice call, the mobile terminal will switch to a 2G/3G network. LTE network can not provide services through Circuit Switch (CS) domain. Data services, such as short messages, can be transmitted through LTE Packet Switch (LTE PS) domain. LTE-compatible mobile terminals may switch to the 3G/2G network through Circuit Switched Fallback (CSFB) or Single Radio Voice Call Continuity (SRVCC), so as to provide voice services.
Supplementary services may be classified into two kinds: Call Dependent Supplementary service and Call Independent Supplementary service (CISS). The Call Dependent Supplementary service refers to a service which is performed in the process of communication, such as call on hold, multi-party communication, etc. The Call Independent Supplementary service (CISS) refers to a service which may not be performed in the process of communication, such as Unstructured Supplementary Service Data (USSD), call forwarding query, call forwarding setting, and call waiting setting, etc.
Nowadays, LTE network can not directly support Call Independent Supplementary service (CISS). However, CISS operations are frequently used by consumers. Falling back to a circuit-switched 3G/2G network for CISS operations will bring unexpected large overheads, which may affect other services and interfere with the user experience.
For example, if CSFB is used to fall back to a circuit-switched 3G/2G network, the process of fallback may be described as follows. Firstly, a User Equipment (UE) initiates a supplementary service request to an LTE network. The LTE network makes a response to the request and triggers the fallback process. However, there exist uncertainties during messages exchange, such as poor quality of LTE network link or low response speed of network. These uncertainties may cause CISS to be delayed for a long time, and even failed. In the meantime, there is a need to process data services of the UE transmitted in the LTE PS domain. These data services may be suspended or may be processed after the mobile terminal falls back to a 3G/2G network.
Typically, CISS operations are transitory and discontinuous. Therefore, if CISS is implemented through CSFB, it is costly and may affect other services in the PS domain which may influence performance of the mobile terminal. Because CISS operations, such as call forwarding setting, call waiting setting and USSD are expected by consumers, improvements are needed. Currently, there is no effective method to implement CISS in an LTE mobile terminal.
The conventional art has the following disadvantages. The conventional LTE network can not provide services in CS domain, and the conventional LTE mobile terminal can not support CISS operations in an LTE network. On the other hand, although the mobile terminal may fall back to a circuit-switched 3G/2G network for CISS implementation through CSFB, the system switch may bring unexpected large overheads, and further adversely influence performances of the network and mobile terminal.
More information may refer to patent application No. US 20120064884 A1. This application provides an LTE-compatible mobile terminal which falls back to other network through CSFB to implement CS domain services.